1. Field of the Invention
The invention in general relates to electric generator monitoring, and particularly to apparatus which will detect a cracked stator coil or other portion of a stator coil water-cooling system.
2. Description of the Prior Art
Modern electric generators such as those driven by steam turbines have the capacity to carry several thousand amperes of current in their stator windings. Such arrangement generates a large amount of heat due to the stator winding resistance as well as rotor winding resistance and windage losses. Accordingly, a cooling system must be provided in order to remove the heat resulting from the electrical and windage losses during normal operation.
One type of cooling system utilizes a flow of cooling gas, such as hydrogen, within the generator housing as well as within the rotor and stator structures to remove the produced heat. In one type of design, a cooling liquid such as water is passed through hollow conductors in the stator coils themselves for cooling purposes. The stator coil water system is a closed circuit which is independent of the hydrogen cooling gas arrangement, with the water within the closed circuit being at a lower pressure than the hydrogen pressure.
If during operation of the electrical generator, a stator coil should crack, hydrogen will find its way into the closed circuit water-cooling system. The closed circuit system includes a water reservoir which is pressurized by a hydrogen gas which may be periodically added and/or vented in order to maintain a predetermined pressure range. The hydrogen in the tank, therefore, may be due to the external hydrogen source or the cooling hydrogen which has leaked in due to a cracked stator coil or other breach of the closed circuit cooling system.
The apparatus of the present invention is operable to determine if there is leakage of hydrogen cooling gas into the water-cooling system which, when coupled with other sensor outputs normally provided in such diagnostic equipment, may be confirmatory of a cracked stator coil.